This invention relates to field of modular electronic assemblies and, more particularly, to enclosures or racks for mechanically and electronically coupling a plurality of printed circuits (p.c.) cards or boards so as to constitute an electronic circuit and to the card guide for aligning and retaining the p.c. boards within such enclosures.
With the advent of printed circuits, many attempts have been made to design enclosures or racks for holding a series of removable, plug-in type p.c. boards. However, many prior enclosure designs have resulted in either substantial initial costs in tooling up to produce the card enclosure or in substantial recurring cost in the manufacturing of the card enclosure components and assembly of the enclosure components into a finished enclosure. Also, many prior enclosure designs do not easily accommodate printed circuit boards of varying sizes or allow for the space between printed circuit boards to be easily varied. One such present enclosure system requires that a plastic card guide with multiple channels, one for each printed circuit board to be retained by the guide, be molded as a unit with the length of the card channel being approximately the length of the printed circuit card and the spacing between card channels being equal to the desired distance between the printed circuit cards within the enclosure. The system has a high initial cost to develop the mold for the card guide and requires a new mold to be designed if the intercard spacing is to be changed or if the length of the p.c. cards is changed. Further, this system may require that multiple card guides be designed and molded if the card guide is not symmetrical such that it can be used for both the top and the bottom guide within the enclosure system.
Another printed circuit card enclosure system of the type described in U.S. Pat. No. 3,696,936 to W. J. Straccia et al, issued Oct. 10, 1972, may be used. In this system, end plates suport metal shelf members which are provided with holes and slots for receiving flexible snap-in card guides which accommodate the printed circuit cards. This system requires a slot and a circular hole to be punched for each flexible card guide used within the enclosure. This system offers more flexibility with respect to the distance between printed circuit cards by allowing the punching of the holes and slots which receive the snap-in card guides to be varied according to the intercard spacing needs as dictated by height of components on the p.c. cards and by electronic cooling requirements. While this manufacturing process produces a card enclosure having the requisite reliability and satisfying all electrical requirements, the manufacturing costs in small production runs are relatively high because of the fact that two different perforations requiring a tool change must be made in the metal shelf to accommodate each snap-in card guide, one perforation being that of a circular hole and the second perforation being that of a slot. Further, this system requires two metal shelf members per level of printed circuit cards used within an enclosure and does not allow for a single shelf member to be shared between adjacent upper and lower levels of printed circuit cards which are arranged in a back-to-back manner.
The instant invention is directed to achieving an improved printed circuit card enclosure system which will satisfy all mechanical and electrical requirements of the application and which will result in a substantial reduction in manufacturing cost. In addition to meeting the mechanical requirements of rigidity and resistance to vibrational stress, the instant invention meets the need of a low-cost printed circuit card enclosure which can be economically manufactured on an assembly line basis or in small production runs.
It is accordingly an object of the present invention to provide a printed circuit card enclosure system having a low initial tooling cost and a low individual unit for assembly-manufacturing cost. The further object is to provide a printed circuit card enclosure system which can be easily modified to accommodate varying size printed circuit cards, varying spacings between printed circuit cards and varying numbers of printed circuit cards within the enclosure.